In the production of hydrocarbons from a wellbore, it is sometimes advantageous to use a hydraulically-actuated pump device which can be circulated into the wellbore; and thereafter a supply of power fluid is connected to the tubing string so that the engine end of the pump device actuates the production end thereof, thereby producing fluid from a hydrocarbon-bearing formation, along with the spent power fluid from the engine.
A specially constructed cavity is usually attached to the lower end of the tubing string and receives the pump assembly therewithin in such a manner that power fluid flows from the surface of the earth, down through the tubing, to the engine end of the pump, while formation fluid flows into the production end of the pump, and produced fluid, along with spent power fluid, is conducted along another flow path to the surface of the earth.
In my previous U.S. Pat. No. 3,517,741, there is disclosed a free-type pump such as discussed above, along with a cavity therefor. In my previous U.S. Pat. No. 3,453,963, there is disclosed an engine end which has proven successful in the production of hydrocarbons from a deep well. In my previous U.S. Pat. No. 4,080,111 there is set forth a production end of the double-acting type which has proven successful in producing hydrocarbons.
It would be desirable to be able to employ a double-acting engine end along with a double-acting production end, and to arrange such a pump assembly so that it is of the free type and can therefore be circulated into and out of the borehole.
It would furthermore be desirable to provide the engine end of such a pump with a closed flow system so that filtered, high pressure power fluid is pumped from the surface of the earth, down the tubing string to the inlet at the engine end of the pump assembly, with the spent power fluid being returned along an isolated flow path and back to the surface of the earth, thereby enabling the power fluid to be maintained separate from the production fluid so that it can be recirculated. The combination of an engine end, production end, and cavity which achieves this desirable attribute is the subject of the present invention.